Enhancing Directional Ion Transport and Ionic Gradient Power by Engineering a Subnano-on-Meso Architecture Based on...

An ion-selective membrane with diode-like properties is a prerequisite for directional ion transport and efficient osmotic power conversion. However, in conventional nanofluidic systems, rectification rapidly deteriorates under high ionic strengths due to severe Debye length screening, which critically limits performance in realistic salinity environments. Here, we report a high-performance mesoscale ionic diode based on a single conical mesochannel selectively modified with a thin porous MXene layer, forming a well-defined porous subnano-on-meso architecture (p-MXene@MC). The pore-engineered MXene simultaneously provides high surface charge while maintaining continuous, low-resistance ion transport pathways, thereby enabling strong rectification even under high ionic strengths. As a result, the p-MXene@MC exhibits a rectification ratio of 7.7-fold at 1 m KCl, and delivers a maximum osmotic power of 697 pW under a 1000-fold KCl gradient, outperforming earlier single-channel osmotic power generators. When protons serve as charge carriers, ultrafast transport within the hydrated porous MXene framework further boosts the power output to ∼1001 pW. The enhanced rectification and energy conversion performance by porous MXene is supported by our simulations based on the Poisson-Nernst-Planck and Navier-Stokes models. This work offers a generalizable strategy for overcoming electrostatic screening and transport limitations in mesoscale channels, paving the way toward practical nanofluidic energy harvesting technologies.